This invention relates to syringe pumps.
Syringe pumps are used to supply medication to a patient. A syringe is pre-filled with the medication and this is connected to an infusion line extending to the patient. The syringe is then loaded in the syringe pump, which applies a force to the plunger of the syringe to drive medication into the infusion line at a controlled rate. The user enters information about the size of the syringe and the dose rate, so that the pump can calculate the drive rate for the plunger to dispense medication at the correct rate.
Syringe pumps may include a syringe barrel sensor, which provides a measure of the diameter of the syringe loaded in the pump. A display is derived from the output from the barrel size sensor so that the user can-check that he has correctly identified the syringe. The Series 3000 syringe pump sold by SIMS Graseby of Watford, England includes a syringe barrel sensor having an arm that is swung into contact with the outside of the barrel. The arm is coupled to a mask that is movable between a row of five LEDs and a row of five photodiodes. The outputs of the photodiodes give an indication of the position of the mask and hence the size of the barrel of the syringe. Such an arrangement gives an approximate indication of the size of the syringe but is not sufficiently accurate to distinguish, for example, between two syringes from different manufacturers having similar external diameters.
It is an object of the present invention to provide an alternative syringe pump.
According to the present invention there is provided a syringe pump including means for mounting a syringe, means for engaging and driving a plunger of the syringe, and a sensor mechanism for sensing the barrel size of the syringe, the sensor mechanism including a contact member displaceable into contact with the outer surface of the barrel, a mask member coupled with the contact member and movable in response to movement of the contact member, and a row of a plurality of optical sensing means positioned to receive radiation transmitted by the mask member, the mask member including a plurality of transmitting regions arranged in a row, each transmitting region having a different length, and the pump including means responsive to the outputs from the sensors to determine the size of the barrel from the combination of the length of the row of sensing means receiving radiation transmitted by one of the transmitting regions and the position of an edge of the transmitting region.
The transmitting regions are preferably transparent apertures in the mask member. The pump may include a radiation source mounted on the same side of the mask member as the sensing means. The pump may include means for collimating radiation falling on the mask member, such as a concave reflector. The contact member is preferably on a swung arm, which may be rotatable about an axis parallel to the axis of the syringe. The mask member is preferably an elongate strip and the row of transmitting regions preferably extends along the length of the strip. The mask member may have five transmitting regions and the row of optical sensing means may be provided by a CCD array. The pump preferably includes information of the barrel size of different syringes such that the syringe type used can be identified from its barrel diameter, and the pump may include a display on which the syringe type is displayed.
A syringe pump according to the present invention will now be described, by way of example, with reference to the accompanying drawings.